Multi-channel processing for high track density optical recording systems

Optical recording is fast becoming popular as a means of achieving high capacity storage for computer and archival storage applications. The mark size and hence the linear density in optical recording is limited by the illumination wavelength and the numerical aperture. Therefore increasing track density by reducing track widths and reducing or eliminating the guard space between data tracks is an important approach towards achieving high areal density. However, decreasing track pitch causes significant intertrack interference in addition to interference within the track, resulting in performance degradation. Multi-track readback of several adjacent tracks using laser-diode arrays and line illumination has been reported in optical recording literature. The high areal density and the multi-track readback can lead to a high data rate. This multi-track readback capability in optical recording also provides a unique opportunity for combined processing of the multi-track readback signals to combat the performance degradation due to the two-dimensional interference.; In this work, we explore different approaches for combined equalization of the multi-track readback signals. Towards this end, a multi-channel model for readback in optical recording is developed. A theoretical framework for design and analysis of multi-channel equalizers is presented. Multi-channel zero forcing equalizer and a new partial response equalizer have been developed and evaluated. A novel method to reduce interference both within and across the tracks using multi-channel decision feedback equalization is also introduced. Evaluations through numerical simulations show significant improvement in bit-error rate performance of the multi-channel equalizers compared to single-channel equalizers (that do not combine the multi-track readback signals) in high areal density systems. The results indicate that multi-channel equalization can be a valuable approach towards achieving the goals of high capacity and high data rate in optical recording systems.